Q-Band ENDOR (Electron Nuclear Double Resonance) of the High-Affinity Ubisemiquinone Center in Cytochrome bo3 from Escherichia coli

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• 作者：Andrei V. Veselov ; Jeffrey P. Osborne ; Robert B. Gennis ; and Charles P. Scholes
• 刊名：Biochemistry
• 出版年：2000
• 出版时间：March 21, 2000
• 年：2000
• 卷：39
• 期：11
• 页码：3169 - 3175
• 全文大小：83K
• 年卷期：v.39,no.11(March 21, 2000)
• ISSN：1520-4995

文摘

Electron nuclear double resonance (ENDOR) was performed on the protein-bound, stabilized,high-affinity ubisemiquinone radical, Q_H^{ages/entities/bull.gif">-}, of bo₃ quinol oxidase to determine its electronic spin distributionand to probe its interaction with its surroundings. Until this present work, such ENDOR studies of protein-stabilized ubisemiquinone centers have only been done on photosynthetic reaction centers whose functionis to reduce a ubiquinol pool. In contrast, Q_H^{ages/entities/bull.gif">-} serves to oxidize a ubiquinol pool in the course of electrontransfer from the ubiquinol pool to the oxygen-consuming center of terminal bo₃ oxidase. As documentedby large hyperfine couplings (>10 MHz) to nonexchangeable protons on the Q_H^{ages/entities/bull.gif">-} ubisemiquinone ring,we provide evidence for an electronic distribution on Q_H^{ages/entities/bull.gif">-} that is different from that of the semiquinonesof reaction centers. Since the ubisemiquinone itself is physically nearly identical in both Q_H^{ages/entities/bull.gif">-} and thebacterial photosynthetic reaction centers, this electronic difference is evidently a function of the localprotein environment. Interaction of Q_H^{ages/entities/bull.gif">-} with this local protein environment was explicitly shown byexchangeable deuteron ENDOR that implied hydrogen bonding to the quinone and by weak proton hyperfinecouplings to the local protein matrix.